1. Field of the Invention
The present invention relates to a base station, a mobile station and a method for data transmission in a communication system, in particular in a CDMA mobile radio system, with the data being transmitted structured into frames in such a manner that it is possible for a mobile station to carry out other functions, in particular to carry out measurements via a receiving device, during one or more interruption phases in which it interrupts the reception (of the previous source or of the data from the base station) and/or the processing of received data or the transmission process. In the following text, the term “transmission” refers to both sending and/or receiving.
2. Description of the Prior Art
In communications systems, data (for example, voice data, image data or system data) are transmitted on transmission paths between base stations and mobile stations. In radio communications systems, this is done with the aid of electromagnetic waves via an air or radio interface. In this case, carrier frequencies are used which lie in the frequency band provided for the respective system. The carrier frequencies for GSM (Global System for Mobile Communication) are in the band around 900 MHz. Frequencies in the frequency band around 2000 MHz are being provided for future radio communications systems, for example the UMTS (Universal Mobile Telecommunication System), which uses a CDMA (Code Division Multiple Access System) method, or other third-generation systems.
Particularly in future CDMA systems, the base station will transmit essentially continuously, for example, in the downlink direction; that is, in the direction from base station to a mobile station. The data transmitted during transmission are normally structured into frames, which each have a predetermined length. The frames may also have a different structure and length, particularly for different services, such as voice data transmission and video data transmission. The structure and/or length of each frame in a continuous sequence of frames is, however, predetermined and/or recognized by the mobile station.
In cellular mobile systems in particular, the mobile station occasionally has to carry out functions other than data reception, which cannot be carried out at the same time, at least when using only a single receiving device. For example, the mobile station in a cellular radio communications system in which the base stations in different cells transmit at different frequencies, from time to time, has to measure whether the radio signals from another base station can be received with good reception quality. To do this, the mobile station sets its receiving device to a different frequency than the frequency at which it is currently receiving data.
In order to allow transmission without interruption from the base station to the mobile station, it has already been proposed for the mobile station to be equipped with a second receiving device. However, this solution is generally rejected in practice for cost reasons.
Another proposal is known from WO-A 9725827, according to which the base station interrupts the transmission at predetermined times in order to allow the receiving station to use its single receiving device to carry out an adjacent channel search or adjacent channel monitoring (search for an adjacent base station or for specific data packets transmitted by these base stations which, in the following text, also may be considered to include synchronization, frequency correction or pilot signal bursts).
In order to avoid loss of data, the base station first of all transmits the data at a higher transmission rate than the essentially constant continuous transmission rate. To prevent this leading to increased bit error rates (BER), the transmission power also needs to be increased during this time.
The frequency at which the interruption phases recur and the length of the interruption phases depend on the respective system and on the respective operating state of the system, as well. Since the deterioration in the transmission quality also increases with the number of interruption phases inserted, it is desirable to insert as few interruption phases as possible, or for the interruption phases to be as short as possible.
An object of the present invention is to specify a method for data transmission in a mobile radio system, a mobile station and a base station, which allows reliable adjacent channel monitoring with a smaller number of interruption phases than in the prior art.